Lithium-ion batteries are just about everywhere—they power almost all smartphones, tablets, and laptops. Yet Elon Musk, CEO of Tesla Motors, says he intends to build a factory in the United States three years from now that will more than double the world’s total lithium-ion battery production. The plan is still in its early stages, but already four states are negotiating with Tesla in the hope of becoming the factory’s home.

People have come to expect bold plans from Musk. In addition to founding Tesla, he started his own rocket company, SpaceX, which now delivers supplies to the International Space Station. But even for him, the “gigafactory,” as he calls it, seems audacious.

First, Tesla sold 23,000 cars last year. The gigafactory, which would start production in 2017, would by 2020 make enough batteries for 500,000 electric cars. (It would produce enough batteries annually to store 35 gigawatt hours of electricity, hence the name). Second, battery companies normally announce factories only after they’re funded and a site is selected. And they typically scale up gradually. Why announce plans to build such an enormous factory —especially when electric car sales so far come nowhere close to justifying it?
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